14S ON THE CAMERA LUCIDA. 



leave a representation of the object barely distinct, for the 

 more complete command of the pencil. 

 Management The whole apparatus remaining stationary, it will be 

 found, that, by moving the head so as to carry the eye far- 

 ther over the prism, and looking inwards, the view will be 

 continued upon the lower part of the paper; and by draw- 

 ing the eye off towards the edge of the prism, and looking 

 the contrary wa) r , the view wiil he continued upwards: thus 

 Fi^Idof view, the reflection of every object comprised within an angle of 

 45° in height and depth will in succession be distinctly seen ; 

 and by a diagonal inclination of the eye towards the right and 

 left a horizontal compass of the landscape equal to an an- 

 gle of 80'' may also be obtained, and iew will be dissatisfied 

 with this field of view. 

 Method of ob- The pencil may now be employed in following the out- 

 taming a dear ]j ne f th e images, and, if their brightness should any where 

 sight of the . '.,.■.' *v. ' . ,. ■ . . „-.'.. 



imageandpen- impede distinct vision or the former at the point ot coinci- 



ril at the same deuce, a slight motion of the eye towards the edge of the 

 time. . ... °, . . , . J , .'•'/-*. 



prism will obtain it, and vice versa when the image is not 



sufficiently distinct. It may not be amiss to recommend 

 generally the near edge of the prism to be kept in a line with 

 the pencil and the image ; for which purpose it will obvi- 

 ously be necessary to move the head in a direction opposite 

 to the motion of the pencil, that the eye may follow it, and 

 keep it in contact with the lower edge of the picture, or 

 rather, the edge of that part of the reflection which is at the 

 instant visible. 

 Directions for When the instrument is used in copying a near or very 



copying a near ta]1 Kj ect \ t mav occasionally be found, that, in following 



*>r -very tall ■> J J ' ' . » 



«bjcct. the image towards the upper part of the paper, the eye will 



be confused with the original reflection, which is coloured 

 -and inverted; it will then be necessary to enlarge the field of 

 view, by turning the prism upon its pm, slightly inclining 

 its face upwards, and depressing the near edge of the stop; 

 which may be done without inconvenience, for, while the 

 };in is strictly confined to a motion in that direction*, the 



* To ensure the confinement of this motion to the vertical direction, a 

 small clamp for the to-,) of the outer stem will be found useful ; this may 

 be tightened as soon as the elevation for the prism is determined on, and 

 w31 answer to prevent the nine; stem from sliding down or turning reuud. 



itaagei 



